The use of recursive filters for reducing noise in video signals is relatively well known. Video recursive filters typically consist of a frame memory, two scaling circuits and an adder circuit. Incoming or current video signal is scaled by one of the scaling circuits and the scaled video signal is applied to one input port of the adder. Signal delayed by substantially one frame period from the output of the frame memory is scaled in the other of the scaling circuits and applied to a second input port of the adder. Video signal sums produced by the adder are coupled to the input of the frame memory and represent noise-reduced video.
The foregoing description applies if the video signal is a monochrome or luminance signal. If the video signal is a chrominance component of composite video a signal chrominance phase inverter must be interposed between the adder circuit and the frame memory. Finally, if the video signal to be processed is composite video, and the desired system output signal is noise reduced composite video signal, then circuitry must be inserted between the adder and frame memory to invert the phase of the chrominance component only, of the noise-reduced composite video signal. An example of this type of video recursive filter is disclosed in U.S. Pat. No. 4,064,530 entitled "Noise Reduction System For Color Television".
A recursive filter, which does not have provision for chrominance phase inversion, and to which composite video is applied tends to produce a noise reduced luminance component with a small amount of residual chrominance contamination after the occurrence of a number of frame periods in which there is no interframe image motion. Thus, a video recursive filter may be employed to partially separate the luminance component from composite video signal for non-moving images. Such a system has limited utility.
It is an object of the present invention to provide luminance/chrominance separation from composite video signal without residual cross components using a recursive filter system.
It is a further object to adaptively control a luminance/chrominance separating recursive filter to rapidly reach steady state operation following cessation of interframe image motion.